1. Field of the Invention
The present invention relates to an apparatus and a method for detecting a heart sound of a living subject, at a position distant from a chest of the subject.
2. Related Art Statement
Heart sounds are used to make a diagnosis of heart-valve disease or congenital heart disease. In addition, heart sounds may be used to obtain pulse-wave-propagation-velocity-relating information such as a pulse-wave propagation needed for a pulse wave to propagate through an artery between two body portions of a living subject, or a pulse-wave propagation velocity at which a pulse wave propagates through an artery.
It has been a conventional manner to detect heart sounds using a microphone. Since heart sounds are vibrations, blood-flow sounds, etc. produced when the valves of the heart open and close, the heart-sound microphone is usually put on the skin of the chest (in particular, the skin right above the heart).
Therefore, when the heart-sound microphone is put on, it is needed to take off cloths to expose the chest. Thus, putting on the heart-sound microphone is more cumbersome than putting on a sensor on an arm or a neck.
Meanwhile, obtaining pulse-wave-propagation-velocity-relating information needs detecting respective heartbeat-synchronous signals at two body portions of a living subject. Therefore, in the case where the heart sound detected by the microphone put on the chest is used as one of the two heartbeat-synchronous signals needed to obtain the pulse-wave-propagation-velocity-relating information, it is disadvantageously needed to put on another sensor on the subject so as to detect the other heartbeat-synchronous signal.